Curable compositions comprising an epoxidised unsaturated polyester and mineral fillers

ABSTRACT

A curable composition includes an unsaturated polyester and an unsaturated monomer copolymerisable with the unsaturated polyester in the presence of polymerisation accelerators and initiators. The unsaturated polyester is an epoxidised unsaturated polyester obtainable by reaction between unsaturated polyester obtainable by reaction between the carboxy end groups of a polyester having unsaturated monomer units and the epoxy groups of an epoxy resin.

The present invention relates to curable compositions consisting of anepoxidised unsaturated polyester, and their use to prepare agglomeratedstones.

The manufacture of agglomerated stone products in which chippings ofmarble, granite, quartz or stone in general, of suitable particle size,are mixed with a chemically or thermally curable binder until reaching asufficient consistency to make the finished product suitable fornumerous uses in the construction industry has long been known.Agglomerates are manufactured industrially by means of variouscompacting technologies, the main ones being vibration andvibro-compressure, which can be performed either at atmospheric pressureor under vacuum.

These materials can be made in the form of tiles, slabs with an area ofover 4 square metres, or blocks with a volume of approximately 3 cubicmetres which are subsequently cut into slabs. The choice of geometry ofthe semi-manufactured product depends on the Mohs hardness of thestarting raw materials, the required appearance of the finished productand the required output of the manufacturing plant.

The development of moulding technology has considerably improved thetechnical and aesthetic properties of the products, because highlyeffective compacting means can be used to mould the finished productwith a drastic reduction in binder.

An unsaturated polyester resin is generally used as binder for technicalreasons of processability and financial reasons associated with itsrelatively low cost, and is sometimes modified by adding specialadditives with specific functions.

The resulting products possess some very interesting technical andaesthetic characteristics, deriving from the quality of the rawmaterials used as mineral fillers and from the fact that the binder,namely unsaturated polyester resin, irreversibly cures under the effectof temperature and/or special reaction initiators.

One of the few but significant drawbacks of using polyester resins asbinders is their limited resistance to attack by alkaline substances,namely chemicals with a pH higher than 7, under certain conditions ofuse, and this obviously affects the chemical resistance of products madefrom unsaturated polyester resins used as raw material.

The reason is that the synthesis of an unsaturated polyester resin, aswill be described in greater detail below, can be genericallyrepresented by the reaction product between a higher alcohol (such aspropylene glycol) and a bifunctional organic acid or an anhydride (suchas maleic or phthalic anhydride), as shown below

wherein R is, for example, the aryl residue of phthalic anhydride or the—CH═CH— residue of maleic anhydride, and m is a value dependent on therequired molecular weight of the polymer.

The polymer thus formed is subsequently mixed with a monomer (such asstyrene) to give a product with the required Theologicalcharacteristics.

The reverse reaction to the esterification described above, calledsaponification (or more generically hydrolysis), is catalysed byalkaline substances in the presence of water, and leads to thedestruction of the polymer and a return to the starting raw materials.

This behaviour by the unsaturated polyester resin means that theproducts made with this raw material have poor chemical resistance,especially to alkaline attack.

“Resistance to chemical attack” herein means the characteristic thatdefines the behaviour of the surface of a covering material in contactwith chemically aggressive agents, ie. those which, in view of theirchemical composition and characteristics, are potentially able to reactwith the surface and corrode it, penetrating into it permanently orotherwise altering its appearance and its physical and mechanicalcharacteristics.

Aggressive chemicals, of acid or basic nature, may be spilt on the floorin an industrial environment, as in the case of oil and grease in amechanical workshop or chemical reagents in an analysis laboratory, ormay constitute liquids which for some reason come into contact with afloor or wall covering in a private dwelling, such as foodstuffs, ink,etc.; they may also be components of cleaning and sanitising productsnormally used for routine or non-routine maintenance of premises.

Finally, it should be borne in mind that most adhesives used to lay walland floor coverings may give rise to alkaline reactions. In particular,the adhesive traditionally used, ie. cement grout, hardens as a resultof the reaction between water and cement powder, developing a basicenvironment (pH between 10 and 12). Under certain conditions of use,such as laying with an excessive amount of reaction water or the use ofpoor quality cement powder, the alkaline reaction that develops duringhardening may attack the agglomerate used as covering, causing damagewhich rises from the laying surface to the visible surface, withefflorescence and discolouring of the surface.

In extreme cases, the damage caused to the structure of the agglomeratedmaterial as a result of the alkaline reaction may lead to breakage anddetachment of the covering material from the base.

The present invention relates to epoxidised unsaturated polyester resincompositions which can be used to make agglomerated stones or systemsconstituted by mineral filers and resins in general, with improvedcharacteristics of chemical resistance, especially to alkaline attack.

The composition of the invention comprise an epoxidised unsaturatedpolyester as defined below, and an unsaturated monomer copolymerisablewith said polyester. The invention also relates to a process for thepreparation of agglomerated stones by using the compositions of theinvention, and to the agglomerated stones thus obtained.

A further aspect of the invention relates to the new epoxidisedunsaturated polyesters or epoxypolyesters.

The epoxypolyesters of the invention are products of condensation of amixture of polycarboxylic acids, especially dicarboxylic acids, andpolyhydroxylic alcohols, in which one of the components is unsaturated,which are subsequently epoxidised with epoxy resins.

The unsaturated dicarboxylic acids or their anhydrides are thosenormally used in the production of unsaturated polyesters, such asfumaric acid, maleic acid, itaconic acid, citraconic acid and maleicanhydride. Unsaturated dicarboxylic acids may be partly substituted bysaturated or aromatic dicarboxylic acids such as isophthalic acid,phthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid,trimellitic acid, adipic acid, succinic acid or azelaic acid or theiranhydrides.

The ratio between unsaturated dicarboxylic acids or their anhydrides andsaturated or aromatic dicarboxylic acids or their anhydrides isgenerally between 0.5 and 1.2.

The glycols used to prepare the polyesters of the invention includeethylene glycol, propylene glycol, diethylene glycol, dipropyleneglycol, propoxylated bisphenol, ethoxylated bisphenol,trimethylolpropane, trimethylolpropane monoallyl ether,trimethylolpropane diallyl ether or mixtures thereof, such as a mixtureof dipropylene glycol, propylene glycol and ethylene glycol in molarratios of between 1:1:0.5 and 1.25:1:0.25.

The epoxy resins used to epoxidise the unsaturated polyesters by meansof the reaction between the carboxyl groups of the polyester and theepoxy groups, are those derived from the reaction bisphenolA—epichlorohydrin, defined by the following general formula:

wherein R′ is the bisphenyl residue of bisphenol A (according to thechemical formula shown below), and n has a value between 0 and 10.

If the —CHCH₃—CH₂— group of the glycol is represented by R″, theepoxidised unsaturated polyester resin has the following chemicalformula:

The value n of the epoxy resin used in the epoxidisation is preferablybetween 0 and 3, corresponding to a molecular weight of between 360 and900.

Epoxidised Novolac resins deriving from the reaction between Novolac andepichlorohydrin can also be used.

Good results in terms of chemical resistance to hydrolysis have alsobeen obtained by adding epoxy adducts, such as glycidyl ester orglycidyl ether, or aliphatic or cycloaliphatic epoxy resins, such asbutanediol, vinyl cyclohexene, dicyclopentadiene diepoxides andmonoepoxides such as p-tert-butylphenyl epoxide to the unsaturatedpolyester.

The epoxy resins preferably used in the invention are those derivingfrom bisphenol A.

Epoxidised polyester solutions in vinyl or acrylic monomers, mixed withmineral and other fillers, cure under the effect of peroxides, andgenerally in combination with curing accelerators. Agglomerates withgood mechanical strength and high resistance to the action of chemicalagents, especially the hydrolytic action of strong alkalis, areobtained, as demonstrated by the examples reported below, with muchhigher resistance values than those obtainable with ordinary polyesterresins.

The polyesters of the invention can be prepared by reacting glycols withsaturated or unsaturated dicarboxylic acids in molar ratios of 1 to 1.2,at a polycondensation temperature of between 180 and 200° C., up to anumber of 0.35–0.45 free carboxyl groups per 1000 parts by weight ofresin. At a second stage, under the action of suitable catalysts (suchas alkyl ammonium salts and alkyl phosphonium salts) a number ofcarboxyl groups is reacted with a number of epoxy groups at temperaturesof between 150 and 200° C. (preferably between 170 and 190° C.) so as toobtain a resin containing between 0.06 and 0.13 free carboxyl groups per1000 parts by weight, equal to an acid number of between 3 and 7.

The amount of bisphenol A-based epoxy resin is 5–14% by weight of theepoxidised polyester. The percentages by weight of bisphenol A which arepresent in the epoxidised polyester resin before dilution in unsaturatedmonomers are between 3 and 9%. These percentages fall to 2–5.8% in theresin diluted with 35% styrene.

The numeric mean molecular weight M_(n) and weighted mean molecularweight M_(w) are calculated on the basis of the following equations:

${\overset{\_}{M}}_{n} = \frac{{\sum{n_{e,i} \cdot M_{e,i}}} + {\sum{n_{g,i} \cdot M_{g,i}}} + {\sum{n_{a,i} \cdot M_{a,i}}} - {18 \cdot P \cdot {\sum n_{a,i}}}}{{\sum n_{e,i}} + {\sum n_{g,i}} + {\sum n_{a,i}} - {2{P \cdot {\sum n_{a,i}}}}}${overscore (M)} _(w) ={overscore (M)} _(n)·(1+P)

wherein n_(e,i), n_(g,i) and n_(a,i) are the numbers of moles of theepoxy resins, glycols and acids respectively, M_(e,i), M_(g,i) andM_(a,i) are the molecular weights of the epoxy resins, glycols and acidsrespectively, and P is the degree of esterification. The degree ofesterification is calculated on the basis of the following equation:

$P = \frac{{{Initial}\mspace{14mu}{acid}\mspace{14mu}{number}} - {{Final}\mspace{14mu}{acid}\mspace{14mu}{number}}}{{Initial}\mspace{14mu}{acid}\mspace{14mu}{number}}$

The weighted mean molecular weights M_(w) are obtained by GPC (GelPermeation Chromatography) analysis, characterised as follows:

Detector UV 254 nm Flow rate 1 ml/min. Solvent tetrahydrofuran Columns1st column 5 μm Hypergel OP10 2nd column 5 μm Hypergel OP25

The values obtained for the epoxidised polyester are approximately twiceas large as those obtainable with non-epoxidised polyester resins.Unexpectedly, the viscosity of the epoxidised polyester diluted instyrene is almost equal to the viscosity of the non-epoxidised polyesterat the same dilution.

The epoxidised polyesters of the invention can be cured at roomtemperature or at relatively high temperatures like ordinarynon-epoxidised polyesters, using peroxides or hydroperoxides such asmethyl ethyl ketone peroxide, cyclohexanone peroxide and benzoylperoxide in amounts ranging between 0.5 and 4 parts per 100 parts byweight of the sum of the epoxidised polyester and the diluting monomeror monomers. The amount of diluting monomers is between 0.25 and 0.7parts per part by weight of the epoxidised polyester, and preferablybetween 0.30 and 0.40.

The dilution monomer is preferably styrene or another unsaturatedmonomer able to react with ordinary unsaturated polyesters such as vinyltoluene, α-methyl styrene, methyl methacrylate and vinyl cyclohexene.

Examples of suitable curing accelerators are metal salts such as cobalt,vanadium and vanadyl salts, and others commonly used to cure unsaturatedpolyesters. Metal accelerators are used at the rate of 0.1–1 parts (asmetal) per 100 parts by weight of the epoxidised polyester dissolved inthe monomer.

Unsaturated polyesters in styrene based on polyglycols, phthalicanhydride and maleic anhydride have unsatisfactory resistance toalkalis. Even if phthalic anhydride is replaced with isophthalic acidand maleic anhydride with fumaric acid, there is no satisfactoryimprovement. Polyesters based on propoxylated bisphenol and fumaric acidhave good resistance to alkalis but are not cheap, and have highviscosities and curing times unsuitable for agglomerate manufacture.

Epoxidised polyesters dissolved in styrene and suitably cured have highmechanical characteristics and, surprisingly, much greater resistance tostrong alkalis than non-epoxidised polyesters.

The same results relating to alkali resistance are obtained for allcurable mixtures consisting of epoxidised polyester resin and mineralfillers used as raw materials.

In particular, excellent chemical resistance results can be obtainedwith agglomerates made using epoxidised polyester as binder, withoutprejudicing any of the physico-mechanical characteristics of thefinished product.

Stone agglomerates can be prepared from mineral fillers of carbonateorigin (such as marble, limestone or stone in general) or siliceousorigin (such as granite or quartz) mixed with epoxidised polyester inpercentages of between 4 and 12% by weight.

Any functional additives which may be required for the process or thoseable to give the finished product particular properties (such as UVstabilisers, adhesion promoters, etc.) are as compatible with theepoxidised polyester resin as with the conventional unsaturatedpolyester resin.

The processes of mixing and subsequent curing of the mixtures are thesame as used with conventional unsaturated polyester resins, as is themoulding process, which can be performed by pressing, vibration orvibro-compressure, either at atmospheric pressure or under vacuum.

The following examples illustrate the invention in greater detail.

EXAMPLE 1

787 parts by weight (5.864 moles) of dipropylene glycol, 341 parts byweight (3.21 moles) of diethylene glycol and 447 parts by weight (5.866moles) of polypropylene glycol are loaded into the reactor. 978 parts byweight (6.599 moles) of phthalic anhydride and 687 parts by weight (7.01moles) of maleic anhydride are added under stirring. The mass isgradually heated in an inert atmosphere to esterification temperature,in the range 160–210° C. The temperature increase is regulated so as tokeep the temperature at the head of the column between 100 and 102° C.,to prevent losses of glycol. When the degree of esterification is84–86%, at which 205–210 parts of reaction water develop, the reactionis carried out at 190–200° C., applying a pressure of 10–20 mmHg (vacuumof 740–750 mmHg), until a 94.5–95.5% degree of esterification isreached, corresponding to:

acid number   22–25 amount of reaction H₂O (theoretical)  231–234 partsnumber of free carboxyl groups (mmols/g of resin) 0.39–0.45

When these values have been reached, the pressure of the apparatus isbrought to atmospheric pressure, and the mass cooled to 170–190° C. Atthis temperature the catalyst, alkyl ammonium salt (0.03% of the reagentmass), and 180 parts of epoxy resin (molecular weight 380, in thegeneral formula n=0.13), equal to 0.9473 epoxide groups, are loaded.

The reaction is carried out until 0.14–1.18 free carboxyl groups areobtained, corresponding to an acid number of 8–10.

After the addition of inhibitors (toluene hydroquinone or hydroquinone,100 ppm) the mixture is dissolved in a sufficient amount of styrene toobtain a 35% styrene content. The epoxidised resin dissolved in styrenethus obtained undergoes the characterisation shown in the table.

EXAMPLE 1 CHEMICO-PHYSICAL CHARACTERISTICS Numeric mean molecular weight{overscore (M)}_(n) ⁽¹⁾ 3100 Weighted mean molecular weight {overscore(M)}_(w) ⁽¹⁾ 6200 Numeric mean molecular weight {overscore (M)}_(n)(experimental) 2698 Weighted mean molecular weight {overscore (M)}_(w)(experimental) 12533 Final acid number 6 % styrene 34 Viscosity at 25°C., mPa · s 580 CHARACTERISTICS OF CURED RESIN⁽²⁾ Flexural strength(ASTM 790/92), Mpa 94 ± 6 Modulus of elasticity, Mpa 2900–3100 ⁽¹⁾Values calculated on the basis of the formulas reported above. ⁽²⁾Curingconditions: 100 parts resin, 0.2 parts 6% cobalt octoate and 2 partsmethyl ethyl ketone peroxide. Post-curing: 24 hrs at room temperature, 2hrs at 80° C. and 1 hr at 90° C.

EXAMPLE 2

The procedure as described in Example 1 was repeated, but with aglycol/anhydride molar ratio of 1.04.

EXAMPLE 2 CHEMICO-PHYSICAL CHARACTERISTICS Numeric mean molecular weight{overscore (M)}_(n) ⁽¹⁾ 2800 Weighted mean molecular weight {overscore(M)}_(w) ⁽¹⁾ 5600 Numeric mean molecular weight {overscore (M)}_(n)(experimental) 2192 Weighted mean molecular weight {overscore (M)}_(w)(experimental) 8951 Final acid number 8 % styrene 36 Viscosity at 25°C., mPa · s 600 CHARACTERISTICS OF CURED RESIN⁽²⁾ Flexural strength(ASTM 790/92), MPa 90 ± 5 Modulus of elasticity, Mpa 2900–3200 ⁽¹⁾Values calculated on the basis of the formulas reported above. ⁽²⁾Curingconditions: 100 parts resin, 0.2 parts 6% cobalt octoate and 2 partsmethyl ethyl ketone peroxide. Post-curing: 24 hrs at room temperature, 2hrs at 80° C. and 1 hr at 90° C.

EXAMPLE 3

The procedure as described in Example 1 was repeated, but using aglycol-anhydride molar ratio of 1.04 and a molar ratio betweendicarboxylic acids or their saturated or unsaturated anhydrides of 0.69.When the required acid number had been reached, 160 parts by weight ofepoxy resin were added.

EXAMPLE 3 CHEMICO-PHYSICAL CHARACTERISTICS Numeric mean molecular weight{overscore (M)}_(n) ⁽¹⁾ 2900 Weighted mean molecular weight {overscore(M)}_(w) ⁽¹⁾ 5700 Numeric mean molecular weight {overscore (M)}_(n)(experimental) 2373 Weighted mean molecular weight {overscore (M)}_(w)(experimental) 11400 Final acid number 8 % styrene 36 Viscosity at 25°C., mPa · s 520 CHARACTERISTICS OF CURED RESIN⁽²⁾ Flexural strength(ASTM 790/92), Mpa 92 ± 2 Modulus of elasticity, Mpa 2900–3100 ⁽¹⁾Values calculated on the basis of the formulas reported above. ⁽²⁾Curingconditions: 100 parts resin, 0.2 parts 6% cobalt octoate and 2 partsmethyl ethyl ketone peroxide. Post-curing: 24 hrs at room temperature, 2hrs at 80° C. and 1 hr at 90° C.

EXAMPLE 4

The procedure as described in Example 1 was repeated, but using aglycol-anhydride molar ratio of 1.04 and a molar ratio betweendicarboxylic acids or their saturated or unsaturated anhydrides of 0.50.When the required acid number had been reached, 150 parts by weight ofepoxy resin were added.

EXAMPLE 4 CHEMICO-PHYSICAL CHARACTERISTICS Numeric mean molecular weight{overscore (M)}_(n) (1) 2900 Weighted mean molecular weight {overscore(M)}_(w) (1) 5700 Numeric mean molecular weight {overscore (M)}_(n)(experimental) 2337 Weighted mean molecular weight {overscore (M)}_(w)(experimental) 10555 Final acid number 8 % styrene 35 Viscosity at 25°C., mPa · s 500 CHARACTERISTICS OF CURED RESIN⁽²⁾ Flexural strength(ASTM 790/92), MPa 84 ± 4 Modulus of elasticity, MPa 2400–2800 ⁽¹⁾Values calculated on the basis of the formulas reported above. ⁽²⁾Curingconditions: 100 parts resin, 0.2 parts 6% cobalt octoate and 2 partsmethyl ethyl ketone peroxide. Post-curing: 24 hrs at room temperature, 2hrs at 80° C. and 1 hr at 90° C.Characteristics of Agglomerates

The epoxidised polyester resins obtained in Examples 1, 2, 3 and 4 wereused to manufacture stone agglomerates prepared by compacting a mixture

epoxidised polyester resin  7.6% (by weight) marble powder 29.0% marblechippings 63.3% colouring paste  0.1%

The mixing sequence was as follows:

-   -   marble chippings    -   epoxidised polyester resin+colouring paste    -   marble powder.

The moulding process was performed by vibro-compressure of the mixtureunder vacuum.

The cross-linking conditions of the resin were:

-   -   100 parts epoxidised resin    -   0.2 parts 6% cobalt octoate    -   2 parts 1:1 mixture of methyl ethyl ketone peroxide and acetyl        acetone peroxide.

Curing was performed for 24 hours at room temperature, followed by 2hour post-curing at 80° C.

The results of the alkali resistance tests (evaluated as the decline inmechanical properties) performed on agglomerates prepared in accordancewith the formulation described above are reported in the table below.The values obtained with an agglomerate prepared under the sameconditions with a conventional unsaturated polyester resin are shown inthe first column for the sake of comparison.

Polyester Resin Resin Resin Resin Mpa Resin Example 1 Example 2 Example3 Example 4 Flexural strength 31 ± 1 30 ± 1 31 ± 1 32 ± 1 30 ± 1 Modulusof elasticity (30 ± 2) × 10³ (30 ± 1) × 10³ (30 ± 1) × 10³ (29 ± 1) ×10³ (28 ± 1) × 10³ Flexural strength after 18 ± 1 27.0 ± 0.5 26.5 ± 0.527.9 ± 0.5 25.7 ± 0.2 72 hours in 10% NaOH Flexural strength after 10 ±1 21 ± 2 20 ± 1 21 ± 1 19 ± 1 192 hours in 10% NaOH Flexural strengthafter  2.5 ± 0.1 14 ± 1 12 ± 1 13 ± 1 11 ± 1 500 hours in 10% NaOH

1. A curable composition comprising an unsaturated polyester and anunsaturated monomer copolymerisable with said unsaturated polyester inthe presence of polymerization accelerators and initiators,characterised in that the unsaturated polyester is an epoxidisedunsaturated polyester obtained by reaction between the carboxy endgroups of a polyester comprising unsaturated monomer units and the epoxygroups of an epoxy resin, wherein the unsaturated monomer units of thepolyester are obtained by reacting a glycol with unsaturatedpolycarboxylic acids or their anhydrides, and wherein the glycol is amixture of dipropylene glycol, propylene glycol and ethylene glycol inmolar ratios of between 1:1:0.5 and 1.25:1:1.25.
 2. The composition asclaimed in claim 1, wherein the epoxy resin is a resin obtained frombisphenol A and epichlorohydrin, epoxidised Novolac resins obtained fromthe condensation of phenol or alkylphenol and formaldehyde withepichlorohydrin, cycloaliphatic or aliphatic epoxy resins obtained byepoxidation with peracetic acid.
 3. The composition as claimed in claim2, wherein the epoxy resin is a resin of epichlorohydrin-bisphenol Awith the formula:

wherein R′ is the bisphenyl residue of bisphenol A (according to thechemical formula shown below), and n has a value between 0 and
 10.


4. The composition as claimed in claim 3, wherein the epoxi-resin has amolecular weight of between 360 and
 900. 5. The composition as claimedin claim 1, wherein the epoxidised unsaturated polyester has a number offree carboxyl groups between 0.06 and 0.13 per 1000 parts by weight,equal to an acid number of between 3 and
 7. 6. The composition asclaimed in claim 5, wherein the unsaturated monomer is selected fromstyrene, vinyl toluene, amethyl styrene, methyl methacrylate and vinylcyclohexene.
 7. The composition as claimed in claim 6, wherein themonomer is styrene.
 8. The composition as claimed in claim 6, whereinthe monomer is present in an amount of between 0.25 and 0.7 parts byweight per part by weight of epoxidised polyester.
 9. The composition asclaimed in claim 7, wherein the monomer is present in an amount ofbetween 0.25 and 0.7 parts by weight per part by weight of epoxidisedpolyester.